Skip to main content

Full text of "The Cambridge Natural History"

See other formats

56                             CUSP NOMENCLATURE

even earlier representatives of these families. Fig. 3G (p. 51)
illustrating a series of mammalian teeth will illustrate the above
remarks. That there is such a convergence in tooth structure
shows that it is, theoretically at least, possible to determine the
ancestral form of the mammalian tooth. Practically, however,
the difficulties which beset such theorising are great ; that there
are such divergent and such strongly-held antithetical views is
sufficient proof of this. Two
main views hold the field:
one, which has found most
favour in America, and is due
chiefly to the labours and per-
suasiveness of Professors Cope,
FIG. 38.—Molar teeth of A, Phenacodus, and   Scott,   Osborn,    and   Others,   is
B, the Creodont Pcdaeonictis.    JSnd, endo-                                    .                    „ ,
conid;    hid,    hypocoimlid ;    hyd>    hypo-    K11OWI1      as       trituberculy.
The aite™tive ™^-as ursed
by Forsyth Major, Woodward,
and G-oodrich, attempts to show that the dentition of the
original niammal included grinding teeth which were multi-
cuspidate or "multitubercular." There is much to be said for
both views, and something to be said against both.
This question is, however, wrapped up in a wider one. Its
solution depends upon the ancestry of mammals. If the Mam-
malia are to be derived from reptiles with simple conical teeth,
then the first stage in the' development of trituberculy is proved.
On the other hand, however, the evidence is gradually growing
that the Theromorpha represent more nearly than any non-
mammalian group with which we are acquainted the probable
ancestral form of the mammals. These animals offer some
support to both the leading views, Cyfn>ogeyict,€hu$ had triconodont
teeth which, as will be pointed out later, are a theoretically
intermediate stage in the evolution of tritubercular teeth; on
the other hand, the teeth of JEHademodon and some others are
multituberculate, and have been very properly compared to the
multitubercular teeth of such primitive mammalia as the Oraitho-
rhynchus. Professor Osborn is no doubt correct in italicising a
remark of an anonymous writer in Science to the effect that in
Dicutemodon the teeth, though multitubercular, show the pre-
valence of three cusps arranged in fclie tritxibereular fashion,
1 Bee for a Btutmaary, Osbom, Atuwrfaaw, Wat, Doc. 1897, p. 993,